The invention relates generally to pressure gauges and more particularly to bourdon tube pressure gauges.
Spring gauges for use in measuring pressure or temperature are well known and have been used commercially for many years. In the case of a Bourdon tube gauge, the measurement element is a tube sealed at a first end and attached to a pressure source to be measured at a second end. U.S. Pat. No. 4,667,517 discloses a Bourdon tube spring element for measuring pressure. Generally, such gauges offer a multitude of uses including applications in the fire protection, medical component, and acetylene welding industries. The spring element is made by compressing through cold working only predetermined areas of a tube wall resulting in a relatively less compressed ridge extending along the length of the tube. This ridge facilitates rapid communication of changes in the pressure source along the length of the tube. Accordingly, response time of the gauge is improved. Unfortunately, the spring gauge requires careful cold working along the entire length of the tube by compression to form the ridge and fails to minimize the volume within the tube and the materials required to produce it.
The invention provides a bourdon tube gauge for measurement of pressure with improved responsiveness to pressure fluctuations, ease of manufacture, and reduced material requirements as compared to conventional pressure gauges. The pressure gauge of the invention includes a spring assembly for connection to a pressure source including a coiled hollow tube having a first end and a second end with a body portion therebetween. The hollow tube is adapted to produce a displacement of the second end in response to a change in the pressure source to which the first end is connected. The second end of the body portion is sealed. The body portion of the spring assembly has a first longitudinal portion and a second longitudinal portion extending from proximate to the first longitudinal portion to the second end. The body portion is substantially uniformly compressed along the second longitudinal portion to thereby reduce the volume of the body portion.
In one embodiment, a transition area is disposed between the first end and the first longitudinal portion of the hollow tube. The transition area is compressed in a manner so as to form a continuous longitudinally extending ridge along said transition area. In another embodiment, the second longitudinal portion is substantially uniformly compressed to form a uniform thickness along the length thereof. The first longitudinal portion and the transition area are partially compressed so as to form a ridge extending along the length of the transition area and the first longitudinal portion.